1. Field of the Invention
The present invention relates to an apparatus for towing a workpiece. More particularly, the present invention relates to a motorized tractor-towing apparatus of enhanced stability capable of towing an airplane, trailer, or other workpiece.
2. Description of the Related Art
It is frequently necessary to move closely-parked private aircraft, for example, around an airfield or within a hanger. State of the art devices disclose tractors having some capability of moving such aircraft but are unstable, particularly when pulling a heavy workpiece, such as an aircraft. See, for example, U.S. Pat. Nos. 3,819,001 and 3,861,483. Because of their unstable nature, such prior art devices require a stabilizer bar or other mechanism to stabilize it and make it more maneuverable particularly in a towing attitude. However, such additional structure makes the prior art devices particularly difficult to operate in congested conditions such as those frequently found at private airfields.
Other prior art aircraft handling and towing devices are cumbersome and do not provide for sharp turning radii required in maneuvering aircraft about a congested airfield, for example. See U.S. Pat. Nos. 3,049,253; 2,732,088; 2,734,716; 3,038,550; 3,662,911; 4,318,448; and 4,576,245.
Additionally, there exists the need for an enhanced gripper mechanism to attach to the nosewheel or tailwheel of an aircraft in a secure manner and yet operate with a small turning radius. Prior art disclosures, such as U.S. Pat. Nos. 2,874,861 and 2,877,911, do not permit the type of gripping necessary for a tight turning radius operation with enhanced locking capability.
Accordingly, the need exists for an improved towing apparatus for aircraft and other workpieces which is stable even when not towing a workpiece. However, once engaged to either a nosewheel or a tailwheel of an aircraft for example, the device provides for a tight turning radius and is easy to maneuver in forward or reverse.
The present invention is an apparatus for towing a workpiece, such as an aircraft. The apparatus comprises first and second frames which are in spaced vertical relationship to one another. The frames are attached in such a manner that the first frame rotates relative to the second frame about a common substantially vertical axis. A wheel assembly is supported by the first frame and includes a wheel for rotational movement about a first axis. A motor is used to power the wheel assembly. A handle assembly is attached to the first frame to enable the operator to rotate the first frame relative to the second frame. A gripper assembly is supported by the second frame and offset from the vertical axis. The gripper assembly is positioned on the second frame to engage a workpiece for towing along a second axis which is positioned above or below the first axis by no more than about 30% of the radius of the wheel. In this manner, the present invention provides a low center of gravity and permits the towing axis, or the working axis, to be at or near the rotating axis of the wheel. Thus, a stable towing apparatus is provided which permits the workpiece, such as the nosewheel or tailwheel of an aircraft, to be in close proximity to the wheel of the present invention. Consequently, the turning radius is small.
The present invention may also include a transmission, such as a hydrostatic transmission, positioned between the motor and the wheel assembly to enable the transmission of power from the motor to the wheel on a smooth basis and permit motorized forward and rearward motion of the towing apparatus and the workpiece.
The gripper assembly of the present invention may be used to tow the nosewheel of an aircraft or another wheel of a workpiece. Alternatively, the gripper assembly may be used to tow the tailwheel of an aircraft. If the nosewheel of an aircraft is being pulled, it may be preferable to permit the nosewheel to remain in contact with the ground while the present invention tows the aircraft. In this event, the gripper assembly is supported by the second frame and includes a stationary arm and a pivotal arm. The pivotal arm is rotated relative to the second frame. Once engaged the ends of both the first and second arms compress the axis of a nosewheel to permit a pulling or pushing towing operation by the present invention. The gripper assembly may also include a gas cylinder, for example, positioned between the first and second arms to dampen any movement between the ends of either arm and the nosewheel thereby further securing the first arm relative to the second arm.
In the event the present invention is intended to engage the tailwheel of an aircraft, the gripper assembly may include a tow frame supporting a cradle. The gripper assembly may include means to tilt one end of the tow frame toward the ground enabling the cradle to engage and support the tailwheel. The gripper assembly may also include means for activating the tilt means to lower one end of the tow frame and then raise that same end thereby elevating the tailwheel off the ground and permitting the present invention to tow the aircraft along a towing axis positioned between about 60% of the radius of the wheel of the present invention above the axis of that wheel to about 60% of the radius of that wheel below the rotational axis of the wheel.
Thus, the present invention provides a stable pushing and pulling towing apparatus for a workpiece such as an aircraft that provides for a sharp turning radius, forward and rear motion, and the introduction of substantial power in a forward or rearward direction on a smooth and continuous basis.
The more important features of this invention have been summarized rather broadly in order that the detailed description may be better understood. There are, of course, additional features of the present invention which will be described hereinafter and which will also form the subject of the claims appended hereto.